The Great Vanishing Oil Spill

The Great Vanishing Oil Spill

Hazen’s team examined one of several plumes of oil droplets emanating from BP’s blowout, and observed rod-shaped bacteria feasting on the 10- to 60-micrometer droplets fast enough to halve the oil every two to six days. That rate contradicts a study of the same plume conducted by the Woods Hole Oceanographic Institution, and published in Science earlier this month, that found meager oxygen consumption (to be expected where large numbers of microbes are consuming oil) and concluded that the oil was therefore not being broken down.

The divergence, according to Hazen, is explained by the thin concentration of the oil. While immense, stretching over 35 kilometers, the oil in the studied plume maxed out at 10 parts-per-million. Oxygen depletion by microbes would thus be negligible, argues Hazen.

In recent weeks, Hazen’s group has detected no oil, although it’s possible the oil could simply have been carried out of view by Gulf currents. Federal incident commander Thad Allen told Technology Review on Wednesday that he needs a more rigorous measurement program to “get a handle on what is actually out there in the water.”

Hazen bets that the dispersed oil has indeed broken down, and says some credit for that goes to the 1.84 million gallons of dispersant sprayed on the spilling oil as part of the cleanup operation. This dispersant also likely acted as a bioremediation agent because the tiny droplets it created gave microbes more surface area to chew at.

Natural microbial activity, however, may fall short in marsh sediments where oil is concentrated and the supply of oxygen and nutrients is constrained, slowing microbial digestion to a crawl.

Artificial enhancements could speed up marsh recovery, says Portier. He says LSU scientists showed this to be true three years ago in a marsh in Lake Charles, LA, that was contaminated with heavy crude. They bolstered the marsh microbial community with an LSU-developed culture of oil-eating marsh microbes, along with diluted fertilizer. After 72 days, untreated sites still harbored more than half of their spilled oil, says Portier, whereas treated sites were clean enough to meet strict federal risk levels for residential areas.

Portier says he is working with a BP-backed research coalition of universities and state agencies that expects to have field trials underway in Gulf marshes next month.